The present invention relates generally to water heaters, and more particularly relates to improvements in the external thermal insulation of hot water storage tank portions of electric water heaters.
In one common form thereof, a modern electric water heater comprises a cylindrical metal tank, in which water to be heated is stored, and one or more electric immersion heating elements extending horizontally through a lower end portion of the tank and having an electrical connector portion disposed on the outer side of the tank. Outwardly circumscribing the tank is a larger diameter cylindrical metal jacket structure that defines around the side surface and top end portions of the tank a hollow insulation space.
In conventionally constructed electric water heaters of this type, a large jacket sidewall opening is circumferentially aligned with the heating element connector portions and vertically extends from a point slightly below the connectors to a point substantially higher than the connectors. Installed outwardly over this large jacket opening is a control panel in an upper portion of which are disposed various electrical control components used to regulate the operation of the immersion heating elements.
With the jacket structure installed outwardly around the storage tank, the water heater is insulated by injecting a suitable foam insulating material into the cavity defined between the jacket structure and the tank. To prevent the injected foam insulation from being forced outwardly through the jacket sidewall opening a fiberglass foam stop block member is suitably affixed to the outer side of the tank, over the heating element connector portions, prior to the installation of the jacket structure and the subsequent injection of the insulating foam.
The installed foam stop block member has a cutout area through which the heating element connector portions are exposed to the jacket sidewall opening. The periphery of the control panel, at its juncture with the outer side surface of the jacket structure, is positioned circumferentially and vertically inwardly of the outer side edge periphery of the foam stop block member, and the periphery of the stop member cutout area is positioned circumferentially and vertically inwardly of the control panel periphery, with the top side edge portion of the cutout area being downwardly spaced a slight distance from the top side of the control panel. Accordingly, an upper portion of the fiberglass foam stop block member is interposed between the panel-mounted control components and the hot side surface of the storage tank.
When the foam is injected into the hollow insulation space between the tank and jacket structure, the outer edge periphery of the foam stop block member serves as a foam barrier to prevent the foam from entering the cutout area and passing outwardly through the large jacket sidewall opening into the control panel. The panel-mounted electrical control components are operatively interconnected with the heating element connector portions by wires that extend from the control components downwardly through the control panel interior and into the foam stop block member cutout area through the jacket sidewall opening.
From an insulation standpoint, this conventional electric water heater construction has two primary disadvantages. First, as previously mentioned, the fiberglass foam stop block member is interposed between the panel-mounted electrical control components and the side surface of the storage tank. Because the fiberglass member has a lower thermal resistivity than that of the injected foam, the control components are undesirably exposed to higher operating temperatures (from the storage tank heat) than they would otherwise be if they were positioned outwardly over the foam insulation.
Second, due to the relative orientations of the control panel, the jacket opening and the foam stop member cutout area, it is necessary to make the height of the stop member quite large relative to the overall height of the water heater. This results in the fiberglass stop member occupying a substantial portion of the insulation space between the storage tank and the jacket structure. Since the thermal resistance of the fiberglass stop member is substantially less than that of the hardened foam insulation, the overall thermal resistivity of the tank insulation system is correspondingly reduced (compared to what it would be if a greater percentage of the insulation cavity was occupied by hardened foam), thereby permitting a greater amount of stored water heat to escape outwardly through the jacket structure.
It can be seen from the foregoing that it would be desirable to provide an electrical water heater, of the general type described above, having an improved tank insulation structure. It is accordingly an object of the present invention to provide such a water heater.